This application is to replace an existing microCAT that already supports multiple NIH-funded projects but is failing and cannot be repaired. The replacement system will support all of the current projects and have higher resolution, faster scan time, and lower radiation dose that will enable new applications, expanding usage to additional research projects. In vivo micro computed tomography systems are used for non-destructive three dimensional analyses of synthetic, ex vivo specimens, and, most importantly, live animals. Two of the four quadrants on our existing microCAT II have failed and cannot be repaired because the manufacturer of that instrument no longer supports parts replacement. The proposed vivaCT80 system is the first and only in vivo microCT system currently available that can produce images at a resolution sufficient for analysis of murine trabecular bone and microvasculature, low radiation dose, and possesses a bore size large enough to accommodate animals as large as small primates. Many current users depend on in vivo microCT for coregistration and attenuation calculations with PET, MRI, and optical CT (FMT, Visen). Hence, the loss of in vivo microCT imaging capabilities will affect multiple imaging platforms and projects across a wide range of biomedical fields. Thus, the vivCT80 will provide years of stable support for existing users and expand numerous, wide ranging, NIH funded projects as well as pilot projects for new users and projects. Supported projects study angiogenesis, skeletal consequences of breast and prostate cancer and multiple myeloma, bone quality, endochondral ossification, Alzheimer's disease, drug development, acute infectious disease, and a range of soft tissue tumors, among others. Aspects of each of these projects either require or will be substantially enhanced by reliable, fast, in vivo microCT imaging. Due to its improved capabilities, the vivaCT80 will undoubtedly foster collaborations within Vanderbilt University and at neighboring institutions. Housing this instrument in the Vanderbilt University Institute for Imaging Science (VUIIS), which has been highly successful in managing numerous imaging modalities, will ensure campus wide access and superior management. Acquisition of a new in vivo microCT is absolutely critical to the continued success of many NIH- funded grants at Vanderbilt.